Why We Need to Change How We Combat Rabies

Why We Need to Change How We Combat Rabies

One person dies of rabies every 15 minutes and another 300 are exposed. Disease ecologist and National Geographic 2015 Emerging Explorer Daniel Streicker is rethinking the way we currently manage bat rabies in his effort to limit the spread of the disease from bats to humans and livestock.

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We've known about bat rabies only for the last hundred
years. As a consequence of that, particularly when we think about vampire bat
rabies we're entering a situation where things are more likely to get worse
before they get better. One person still dies of the disease every 15 minutes and
another 300 are exposed. We're talking about 50,000-60,000 people dying every
year.

When we see images of bats we think about a lot of different
things. These types of like, folkloric and superstitious ideas around bats are
really powerful. So powerful that sometimes they distract us from the reality that
bats are real organisms. They have complex ecologies, complex behaviors and
those ecologies or behaviors are actually critical to the functioning of our
ecosystems. Bats pollinate the agave plants that we use to make tequila. They
disperse seeds, yeah, it's true. They disperse seeds that are critical for our
forests to regenerate. They control the insects that would otherwise devastate
some of our most important food crops. However, more recently when we hear
about bats in the news it's in a different context. It's in the context of emerging
infectious diseases. We now know that viruses like SARS, and even Ebola originated
from bats before they began to infect people. And these diseases and several others
associated with bats do have significant consequences for human health and
livelihoods. If we are going to do anything about these scary new viruses we
need to understand better how viruses work in bat populations and that means
understanding more about how to integrate ecology and biology into disease
control.

The bat species that convinced me of this need to integrate
biology and ecology into infectious disease control is this guy the common
vampire bat. This is a bat that feeds exclusively on blood as the name implies.
And the way that that bat feeds is to make a razor sharp incision into the
animal that it is feeding on and then it uses a specially grooved tongue to lap
up blood. That's not it, because these bats also have anti-coagulants in their
saliva which keep that blood flowing and after they finish eating, they can
just hop up into air which is really unusual for a bat most have to climb up
onto something. But these guys are incredibly agile. So, all of these cool
ecological physiological features of these bats make for great dinner party
conversations. But, they are also quite troubling for public health officials,
veterinarians and disease ecologists like myself because these traits make bats
incredibly good transmitters of rabies virus. Rabies is one of our most ancient
human diseases. We know it as this disease mostly in dogs. It causes them to froth
at the mouth and attack us, bite us savagely and we've known about rabies almost
since the beginning of humankind. Rabies has been described in ancient Chinese
and Arabic texts as an incurable wound resulting from the bite of a rabid
animal. That incurable part of rabies is still true. We still don't have a treatment
for people once they start to show signs of rabies. Even by the most
rudimentary standards that we have now one person still dies of the disease
every 15 minutes and another 300 are exposed. We are talking about 50,000-60,000
people dying every year. Just kind of compare that for reference to the current
Ebola outbreak, which as tragic as it is has killed about 11,000 people. Rabies
is about multiplying that by five but then it's not a one-off thing it's
happening every single year. However, where we have made massive progress in
the last 50 years really is in our vaccination of animals.

This is a photo of a dog rabies campaign in Tanzania. And
these types of campaigns have been done in many parts of the world and they've
really reduced the burden of the disease both for humans and their dogs. Vaccination
has also been a critical component of wildlife rabies control. Here we have
oral rabies vaccines which are integrated into a bait. When the animals eat
these baits they are also vaccinated against rabies. And that has prevented the
westward spread of rabies in raccoons. When we think about bat rabies, however we're
in a really different ballpark. We've known about bat rabies only for the last
hundred years. And that combined with the kind of historical scientific neglect
of bats as a subject of research means that we don't have the same kinds of
tools to control rabies within bat populations. As a consequence of that particularly
when we think about vampire bat rabies we're entering a situation where things
are more likely to get worse before they get better. And, I say that because we're
introducing livestock in lots of places where they didn't used to be. Particularly
in Latin America where you find these bats we are exchanging forests for
pastures. And, for the vampire bats this is probably the best thing that's ever
happened. You just imagine you're a bat and you're used to feeding on relatively
scarce wildlife and all of a sudden you've got a cattle farm right there. That
is a... all you can eat buffet. So, not surprisingly the bats respond. They
respond in larger populations and they respond in being places where they
didn't used to be. So, of course, you get a lot of bat bites on livestock and
this is really troubling for farmers not only because of the damage caused by
the bites themselves but also because many of these bites will result in a
lethal rabies infection. What's perhaps even more disturbing though is that if
you don't have livestock in an area you see pictures like this. This is a young
child who has been bitten on the head by a vampire bat. This is shockingly
common. We go to communities where 50 to 80 percent of households have been
bitten by bats, in the last six months. If you count those bites it adds up to hundreds,
even thousands of bites happening in relatively small areas over a course of
about a year.

The natural response of the people that are affected by this
is to kill bats, and they do that in any number of ways. It can be lighting
caves on fire with gasoline. It can be constructing nets made out of thorns. The
state sanctioned way of killing bats is using a poison called vampiricide. And
that's what is shown in the photo there. Where essentially a poison is mixed
together with Vaseline and that's spread on the back of a bat. They release
that one, it flies back to its roost. And the other ones groom it off, ingest
the poison and die. Sounds straightforward enough. Unfortunately, there's not
really much evidence that it's doing anything to control rabies. In some of the
places where they are doing this culling most intensively we're still seeing
most-- really intense levels of rabies activity in livestock. One of the first
questions that I wanted to ask was why is it that this conventional wisdom that
the only good bat is a dead bat isn't actually doing its purpose. So, in order
to try to answer that question we began sampling bats.

This is a picture of a blood sample being taken from a
vampire bat. And we don't just sample them and kill them we are actually one of
the few groups that samples them marks them and lets them go. And so we've been
monitoring about 30 bat colonies now for the last eight years. And we've gotten
a lot of insights from this work. We found a number of reasons why killing bats
might not be the most appropriate way to go about controlling rabies. The first
possibility is that when we conceive or we think about controlling a bat colony
by killing it we're often doing that after a livestock rabies outbreak occurs. And
our idea is that, okay, a cow died of rabies there must be a bat right out
there, right next door that also has rabies. Unfortunately that's not what we
see in reality. Like any good forest fire rabies doesn't just sit in the same
place year after year. It has to move around a lot on the landscape to get new
fuel which in this case is new bats. So, when we go to a colony after-- by the
time a cow has died the virus is already gone. And so what we're doing when we
cull is to kill off those immune bats. So, that's actually not good. That means
that the next time rabies comes it's more likely to cause an outbreak 'cause
you don't have those individuals protecting you. If we are lucky enough to
actually cull during the process of a rabies outbreak so rabies is still there then
I would argue that we are still very unlikely to actually get rid of the
infected animals. And that's because rabies and bats like it is in many other
species causes a number of different symptoms. It causes them to be withdrawn, lethargic,
perhaps aggressive. So, these are not animals that have the normal social behavior
that would allow them or encourage them to be grooming off their roost mates. So,
I think again we're most likely killing off the wrong animals. The final
complexity I wanted to mention is that bat colonies of course don't exist in
isolation. So when we do cull a colony we're going to change the social
structure and we're going to in particular encourage movement of bats between different
colonies. So that means arrival of some bats to the currently infected colony or
a movement of rabid bats or bats that are incubating rabies to other colonies. That
means transmission, and that means longer and more geographically dispersed
outbreaks. So we can actually see this if we look at patterns of livestock
rabies on the landscape what you are seeing here is a video from southern Peru and
what you are seeing is the virus really jumping around quite a lot on the
landscape. That's not really because of movement of cows. That's because of the
unpredictable movement of bats. So, what we have is a really serious disconnect
here between the way control is done and the way that the disease actually
works at the level of the bat population.

So, this has all been very exciting from a scientific
standpoint... and it really empowers us to be able to speak with government
offices, to speak with local communities and explain the work that we're doing and
the results that we've had. However, it's really not enough just to say what
you've been doing for the last 10-20 years isn't effective. We need to start providing
solutions. So, one of the most, I think, innovative and exciting ideas we've
had in the last, really, six months is whether we can replace the poison that's
used in the vampiricide with an oral rabies vaccine. In Peru, we're in a
spectacular situation to be able to try this. We've recently detected that there
are actually travelling waves of rabies moving down different valleys of the
Andes. So, you can actually see this on the map where the dark points are the
old rabies cases the light points are the new rabies cases. And we see them in
a very step like manner moving through these valleys. That is powerful. That
allows us tell farmers, okay you're going to have rabies. You don't have it
now, but you will in a month you will in six months, you will in a year. That
allows them to make an informed decision about vaccination. Second, this is a really
powerful experimental opportunity. We can consider this valley and there are
several others like it we can consider these as experimental replicates. Can we
try vaccinating at various stages in the valley or across different valleys and
compare that with other types of interventions. And say what works, what
doesn't... can we use science to figure this out?

So, I would love to come back here and... in a year or two
and tell you fantastic results from this vaccination experiment. However, I
think as scientists we need to be aware that there's probably not going to be a
one-size-fits-all solution. We may not get it right the first time. This is
true for rabies. It's true for Ebola, SARS, MERS, you name it. We need to
really embrace this idea of a scientific process in making disease control
interventions. I think that's the way forward. And that's really the roadmap to
getting sustainable solutions in disease control of wildlife. Thanks.

Why We Need to Change How We Combat Rabies

One person dies of rabies every 15 minutes and another 300 are exposed. Disease ecologist and National Geographic 2015 Emerging Explorer Daniel Streicker is rethinking the way we currently manage bat rabies in his effort to limit the spread of the disease from bats to humans and livestock.

The National Geographic Live series brings thought-provoking presentations by today’s leading explorers, scientists, photographers, and performing artists right to you. Each presentation is filmed in front of a live audience at National Geographic headquarters in Washington, D.C. New clips air every Monday.

Join us online to see more from National Geographic Explorers! :FacebookTwitter